Study of a Single Dose or Two Doses of a Trivalent Inactivated Influenza Vaccine Produced at Shenzhen, China

Inclusion Criteria: * Aged ≥ 6 months on the day of inclusion * Informed Consent Form has been signed and dated: * by the parent(s) or legally acceptable representative, if applicable, for subjects \<18 years of age. Additionally, an assent form has been signed by the subject if aged 10 to 17 years (based on local regulations). * by the subject himself/herself for subjects ≥18 years of age. * Subject and parent(s)/legally acceptable representative (if applicable) are able to attend all scheduled visits and to comply with all trial procedures * For subjects aged 6-35 months only: Born at full term of pregnancy (≥37 weeks) and with a birth weight ≥2.5 kg * For subjects aged 3-8 years only: Subject has previously received at least one dose of influenza vaccine in the past years or has a history of prior exposure to influenza virus through natural infection. Exclusion Criteria: * Subject is pregnant (positive urine pregnancy test), or lactating, or of childbearing potential (to be considered of non-childbearing potential, a female must be pre-menarche or post-menopausal for at least 1 year, surgically sterile, or using an effective method of contraception or abstinence from at least 4 weeks prior to vaccination and until at least 4 weeks after vaccination) * Participation at the time of study enrollment (or in the 4 weeks preceding the first trial vaccination) or planned participation during the present trial period in another clinical trial investigating a vaccine, drug, medical device, or medical procedure * Receipt of any vaccine or planned receipt of any vaccine within the period from 2 weeks before to 2 weeks after trial vaccination (subjects aged ≥3 years) or within the period from 2 weeks before the first trial vaccination to 2 weeks after the second trial vaccination (subjects aged 6-35 months) * For subjects aged 6-35 months only: Previous vaccination against influenza (i.e. 2 consecutive doses of influenza vaccine \[same seasonal strain composition\]) any time prior to study enrollment or history of prior exposure to influenza virus through natural infection * Vaccination against influenza given in the past 6 months with any influenza vaccine or planned receipt of influenza vaccination during the present study * Receipt of immune globulins, blood or blood-derived products in the past 3 months, which might interfere with assessment of the immune response * Known or suspected congenital or acquired immunodeficiency; or receipt of immunosuppressive therapy, such as anti-cancer chemotherapy or radiation therapy, within the preceding 6 months; or long-term systemic corticosteroid therapy (prednisone or equivalent for more than 2 consecutive weeks within the past 3 months) * Reported history of seropositivity for Human Immunodeficiency Virus (HIV), after questioning the subject or the subject's parents or another legally acceptable representative * Known systemic hypersensitivity to eggs, chicken proteins, neomycin, formaldehyde and octoxynol-9, or to any of the vaccine components, or history of a life-threatening reaction to the vaccine used in the study or to a vaccine containing any of the same substance * Self-reported thrombocytopenia, as reported by the subject, parent or legally acceptable representative contraindicating intramuscular vaccination * Bleeding disorder, or receipt of anticoagulants in the 3 weeks preceding inclusion, contraindicating intramuscular vaccination upon investigator's judgment * Deprived of freedom by an administrative or court order, or in an emergency setting, or hospitalized involuntarily * Current alcohol abuse or drug addiction that might interfere with the ability to comply with trial procedures * Chronic illness that, in the opinion of the investigator, is at a stage where it might interfere with trial conduct or completion * Moderate or severe acute illness/infection (according to investigator judgment) on the day of vaccination or febrile illness (axillary temperature ≥37.1°C). A prospective subject should not be included in the study until the condition has resolved or the febrile event has subsided * Receipt of oral or injectable antibiotic therapy within 72 hours prior to the first blood draw * Identified as an Investigator or employee of the Investigator or study center with direct involvement in the proposed study, or identified as an immediate family member (i.e., parent, spouse, natural or adopted child) of the Investigator or employee with direct involvement in the proposed study.